1. Field of the Invention
The present invention relates to a large scale cell harvesting method, particularly to a large scale cell harvesting method for pack-bed culture device.
2. Description of the Prior Art
Large-scale cell culture processes have been developed extensively over the years for the growth of bacteria, yeast and molds, all of which typically possess robust cell walls and/or extra cellular materials thus, are more resilient. The structural resilience of these microbial cells is a key factor contributing to the rapid development of highly-efficient cell culture processes for these types of cells. For example, bacterial cells can be grown in very large volumes of liquid medium using vigorous agitation, culture stirring and gas sparging techniques to achieve good aeration during growth while maintaining viable cultures. In contrast, the techniques used for culturing cells such as eukaryotic cells, animal cells, mammalian cells and/or tissue are more difficult and complex because these cells are much more delicate and fragile than microbial cells. These cells can be easily damaged by excessive shear forces that may be resulted from vigorous aeration and agitation required for microbial cultures in conventional bioreactors.
Referring to FIG. 1, which is a schematic diagram illustrating a packed-bed culture devices of the prior art. Packed-bed bioreactor 1.1 contains porous matrices 1.3 for cell growth and protects cells from shear. Due to the matrices provide high surface area, cell density can be higher than the other systems. Usually a density of 5˜10×107 cells/ml matrix can be easily achieved. However, due to the packed-bed functions as a depth filter and is unable to mix after the liquid enter the packed-bed, inoculums are trapped along the flow path through the packed-bed and result a heterogeneous and gradient distribution 1.4 of the cells in the packed-bed.
During culture, nutrient and oxygen also consumed and depleted along with the flow path in the packed-bed so that the oxygen and nutrient is rich at the beginning and is low or depleted at the end of the flow path. All above reasons cause heterogeneous growth of cells in the packed-bed bioreactor and retard the scale up capability in traditional packed-bed bioreactor. However, cell harvest is another important issue in packed-bed bioreactor. Cells are usually difficult to detach from the porous matrices in the packed-bed bioreactor since it is very difficult to apply agitation inside the matrix bed which is essential for cells detaching from the matrices after trypsinization. Therefore, cell source such as inoculums for packed-bed cell culture system usually have to be provided with other cell culture devices, such as tissue culture flasks, roller bottles, cell factory, microcarrier stir tank system, etc. Numbers of cell culture devices are required to collect enough inoculums for seeding in the packed-bed bioreactor. It is tedious and posts the risks to be contaminated during cell harvest process.
To make the scale up of packed bed system become more efficient, a cell harvest system that could harvest cells directly from one packed-bed system and transfer them to another larger scale packed-bed system may make the packed-bed system become a vessel to vessel close transfer system. It may then be able to reduce the risk and labor cost to prepare the inoculums. Therefore, the scale up of packed-bed bioreactor may no longer rely on other cell culture devices.
Another issue when cells were cultured in different culture systems with different culture principle, which might cause the change of cell characteristics. A scale up process using similar culture principle device could alleviate the doubt on altering cell behaviors, which might affect the outcome from the cell culture process.
Therefore, it is now a current goal to develop a method and a packed-bed cell culture device that enables cell harvest from the said device.